Asthma is a disease in which (i) bronchoconstriction, (ii) excessive mucus production, and (iii) inflammation and swelling of airways occur, causing widespread but variable airflow obstruction thereby making it difficult for the asthma sufferer to breathe. Asthma is a chronic disorder, primarily characterized by persistent airway inflammation. However, asthma is further characterized by acute episodes of additional airway narrowing via contraction of hyper-responsive airway smooth muscle.
Asthma is managed pharmacologically by: (1) long term control through use of anti-inflammatories and long-acting bronchodilators and (2) short term management of acute exacerbations through use of short-acting bronchodilators. Both of these approaches require repeated and regular use of the prescribed drugs. High doses of corticosteroid anti-inflammatory drugs can have serious side effects that require careful management. In addition, some patients are resistant to steroid treatment. The difficulty involved in patient compliance with pharmacologic management and the difficulty of avoiding stimulus that triggers asthma are common barriers to successful asthma management.
Current management techniques are neither completely successful nor free from side effects. Presently, a new treatment for asthma is showing promise. This treatment comprises the application of energy to the airway smooth muscle tissue. Additional information about this treatment may be found in commonly assigned patents and applications in U.S. Pat. Nos. 6,411,852, 6,634,363 and U.S. published application nos. US-2005-0010270-A1 and US-2002-0091379-A1, the entirety of each of which is incorporated by reference.
The application of energy to airway smooth muscle tissue, when performed via insertion of a treatment device into the bronchial passageways, requires navigation through tortuous anatomy as well as the ability to treat a variety of sizes of bronchial passageways. As discussed in the above referenced patents and applications, use of an RF energy delivery device is one means of treating smooth muscle tissue within the bronchial passageways.
FIG. 1A illustrates a bronchial tree 90. As noted herein, devices treating areas of the lungs must have a construction that enables navigation through the tortuous passages. As shown, the various bronchioles 92 decrease in size and have many branches as they extend into the right and left bronchi 94. Accordingly, an efficient treatment requires devices that are able to treat airways of varying sizes as well as function properly when repeatedly deployed after navigating through the tortuous anatomy.
Tortuous anatomy also poses challenges when the treatment device requires mechanical actuation of the treatment portion (e.g., expansion of a treatment element at a remote site). In particular, attempting to actuate a member may be difficult in view of the fact that the force applied at the operator's hand-piece must translate to the distal end of the device. The strain on the operator is further intensified given that the operator must actuate the distal end of the device many times to treat various portions of the anatomy. When a typical device is contorted after being advanced to a remote site in the lungs, the resistance within the device may be amplified given that internal components are forced together.
It is also noted that the friction of polymers is different from that of metals. Most polymers are viscoelastic and deform to a greater degree under load than metals. Accordingly, when energy or force is applied to move two polymers against each other, a significant part of friction between the polymers is the energy loss through inelastic hysteresis. In addition, adhesion between polymers also plays a significant part in the friction between such polymers.
In addition to basic considerations of navigation and site access, there exists the matter of device orientation and tissue contact at the treatment site. Many treatment devices make contact or are placed in close proximity to the target tissue. Yet, variances in the construction of the treatment device may hinder proper alignment or orientation of the device. For example, in the case of a device having a basket-type energy transfer element that is deployed intralumenally, the treatment may benefit from uniform contact of basket elements around the perimeter of the lumen. However, in this case, design or manufacturing variances may tend to produce a device where the angle between basket elements is not uniform. This problem tends to be exacerbated after repeated actuation of the device and/or navigating the device through tortuous anatomy when the imperfections of the device become worsened through plastic deformation of the individual components. Experience demonstrates that once a member becomes predisposed to splaying (i.e., not maintaining the desired angular separation from an adjacent element), or inverting (i.e., buckling inward instead of deploying outward), the problem is unlikely to resolve itself without requiring attention by the operator. As a result, the operator is forced to remove the device from the patient, make adjustments, then restart treatment. This interruption tends to increase the time of the treatment session.
As one example, commonly assigned U.S. Pat. No. 6,411,852, incorporated by reference herein, describes a treatment for asthma using devices having flexible electrode members that can be expanded to better fill a space (e.g., the lumen of an airway.) However, the tortuous nature of the airways was found to cause significant bending and/or flexure of the distal end of the device. As a result, the spacing of electrode members tended not to be even. In some extreme cases, electrode elements could tend to invert, where instead of expanding an electrode leg would invert behind an opposing leg.
For many treatment devices, the distortion of the energy transfer elements might cause variability in the treatment effect. For example, many RF devices heat tissue based on the tissue's resistive properties. Increasing or decreasing the surface contact between the electrode and tissue often increases or decreases the amount of current flowing through the tissue at the point of contact. This directly affects the extent to which the tissue is heated. Similar concerns may also arise with resistive heating elements, devices used to cool the airway wall by removing heat, or any energy transfer device. In any number of cases, variability of the energy transfer/tissue interface causes variability in treatment results. The consequential risks range from an ineffective treatment to the possibility of patient injury.
Furthermore, most medical practitioners recognize the importance of establishing acceptable contact between the transfer element and tissue. Therefore, distortion of the transfer element or elements increases the procedure time when the practitioner spends an inordinate amount of time adjusting a device to compensate for or avoid such distortion. Such action becomes increasingly problematic in those cases where proper patient management limits the time available for the procedure.
For example, if a patient requires an increasing amount of medication (e.g., sedatives or anesthesia) to remain under continued control for performance of the procedure, then a medical practitioner may limit the procedure time rather than risk overmedicating the patient. As a result, rather than treating the patient continuously to complete the procedure, the practitioner may plan to break the procedure in two or more sessions. Subsequently, increasing the number of sessions poses additional consequences on the part of the patient in cost, the residual effects of any medication, adverse effects of the non-therapeutic portion of the procedure, etc.
In view of the above, the present methods and devices described herein provide an improved means for treating tortuous anatomy such as the bronchial passages. It is noted that the improvements of the present device may be beneficial for use in other parts of the anatomy as well as the lungs.